c# - 更改 Xamarin Forms 上 ListView 项的背景颜色

Question

我有一个 ListView，它从 ObservableCollection 绑定(bind)它的项目，还有一个 Button，它改变一个特定对象的“Amount”属性那个ObservableCollection。我想更改这些“金额”已更改的 Items 的 BackgroundColor。

我已经为此搜索了解决方案，但找不到。
有人知道解决这个问题的方法吗？

Answer 1

一种方法是添加一个新属性，例如 HasAmountChanged，将视单元的背景颜色绑定(bind)到该属性，并使用 ValueConverter 设置颜色。这看起来像下面这样:

具有属性的对象类:

public class MyObject : INotifyPropertyChanged
{
    double amount;
    bool hasAmountChanged = false;

    public event PropertyChangedEventHandler PropertyChanged;

    public MyObject(double amount)
    {
        this.amount = amount;
    }

    public double Amount
    {
        get => amount;
        set
        {
            if (amount != value)
            {
                amount = value;
                OnPropertyChanged(nameof(Amount));
                HasAmountChanged = true;
            }
        }
    }

    public bool HasAmountChanged
    {
        get => hasAmountChanged;
        set
        {
            if (hasAmountChanged != value)
            {
                hasAmountChanged = value;
                OnPropertyChanged(nameof(HasAmountChanged));
            }
        }
    }

    protected virtual void OnPropertyChanged(string propertyName)
    {
        PropertyChanged?.Invoke(this, new PropertyChangedEventArgs(propertyName));
    }
}

观点。注意 ViewCell 中的堆栈布局，这是设置背景颜色的地方:

<ContentPage xmlns="http://xamarin.com/schemas/2014/forms"
         xmlns:x="http://schemas.microsoft.com/winfx/2009/xaml"
         xmlns:local="clr-namespace:Delete"
         x:Class="Delete.MainPage">

<ContentPage.Resources>
    <ResourceDictionary>
        <local:ListViewBackgroundColorConverter x:Key="ListViewColorConverter" />
    </ResourceDictionary>
</ContentPage.Resources>

<StackLayout>
    <Button Text="Click Me" Clicked="ButtonClicked" />

    <ListView ItemsSource="{Binding MyItemsSource}" HasUnevenRows="True">
        <ListView.ItemTemplate>
            <DataTemplate>
                <ViewCell>
                    <StackLayout Spacing="15" 
                                 BackgroundColor="{Binding HasAmountChanged, Converter={StaticResource ListViewColorConverter}}" 
                                 HorizontalOptions="FillAndExpand" 
                                 VerticalOptions="FillAndExpand">
                        <Label Text="FOO 1"/>
                        <Label Text="{Binding Amount}"/>
                        <Label Text="{Binding HasAmountChanged}" />
                        <Label Text="FOO 4"/>
                    </StackLayout>
                </ViewCell>
            </DataTemplate>
        </ListView.ItemTemplate>
    </ListView>

</StackLayout>

为了完整起见，包含 View 背后的代码:

public partial class MainPage : ContentPage
{
    public ObservableCollection<MyObject> MyItemsSource { get; set; }

    public MainPage()
    {
        InitializeComponent();

        MyItemsSource = new ObservableCollection<MyObject>
        {
            new MyObject(1.14),
            new MyObject(1.14),
            new MyObject(1.14),
            new MyObject(1.14),
            new MyObject(1.14),
        };

        BindingContext = this;
    }

    void ButtonClicked(object sender, EventArgs e)
    {
        var rnd = new Random();

        var myObject = MyItemsSource[rnd.Next(0, MyItemsSource.Count)];

        myObject.Amount = 5.09;
    }
}

最后是最重要的部分，转换器:

public class ListViewBackgroundColorConverter : IValueConverter
{
    public object Convert(object value, Type targetType, object parameter, CultureInfo culture)
    {
        return (bool)value ? Color.LawnGreen : Color.DarkRed;
    }

    public object ConvertBack(object value, Type targetType, object parameter, CultureInfo culture)
    {
        throw new NotImplementedException();
    }
}

请注意，您实际上想要检查它是一个 bool 值并处理它。